Patent Application
20210387193
This disclosure relates generally to the field of viscometers and, more particularly, to viscometers for high throughput analysis of fluids.
The importance of viscosity measurements spans many applications including but not limited to consumer products, pharmaceuticals, inks, biological samples, and lubricants. Understanding how these substances resist motion under an applied force enables users to predict how that substance will perform for any given application. Many macroscale rheometers on the market provide the necessary viscosity measurements for common applications. However, these macroscale rheometers tend to be low throughput, high volume, and costly for the user (e.g., these are bulky and require skilled operators). In addition, currently available viscometers require a large sample volume, cumbersome cleaning procedures, are useful for only a limited shear-rate range, are not suitable for complex fluids, and are known to be associated with problems such as viscoelastic skin formation, bubble formation, and evaporation. Pressure sensor-based viscometers are known not to exhibit sufficient durability.
The microfluidic viscometers disclosed herein solve many of these problems. For instance, the microfluidic viscometers disclosed herein have a broad dynamic viscosity range (i.e., 0.1 to 50,000 cP) and shear rate range (e.g., 1-500,000 l/s); provide true multiplex capability (e.g., up to 30 samples may be analyzed simultaneously); small sample volume required (e.g., 5-25 ul); provide highly accurate and reliable data (e.g., 2-5% of reading); highly reproducible readings (e.g., within 1%); provide for wide temperature control (e.g., 4-80° C.); applicable to Newtonian and Non-Newtonian fluids; include disposable cartridges; and include easy-to-use software (e.g., on-board parameter control and data analysis). These and other advantages over currently available rheometers and viscometers will be evident from the disclosure below.
This disclosure relates to microfluidic viscometers and assemblies comprising the same that can be used to determine the viscosity and/or other properties of a fluid. In some embodiments, this disclosure relates to a microfluidic viscometer assembly, the assembly comprising: a) a microfluidic cartridge comprising at least two microfluidic circuits, each microfluidic circuit comprising: an inlet; at least one microfluidic channel comprising: a first channel section having a first diameter and an end in direct fluidic communication with the inlet, and, a second channel section having an optically clear channel subsection, or being completely optically clear, and having a second diameter greater than the first diameter, wherein the second channel section is in direct fluidic communication with the first channel section at an end opposite the inlet; and, an outlet in fluid communication with the second channel section at an end opposite the first channel section, wherein the first channel section provides a resistance to a fluid traversing said microfluidic channel that is at least 80% and less than 100% of a combined resistance of the first and second channel sections, and/or of the microfluidic circuit; b) an image recording system optically connected to the optically clear channel section of the at least two microfluidic circuits; and, c) a pressure control unit, configured to deliver fluid into each of the at least two microfluidic circuits.
In some embodiments, this disclosure relates to a microfluidic viscometer assembly, the assembly comprising: a) a microfluidic cartridge comprising at least two microfluidic circuits, each microfluidic circuit comprising: i) an inlet; ii) an outlet; iii) at least one microfluidic channel comprising at least a first, second and third channel section, wherein: the first channel section is positioned between the second and third channel sections; the second channel section at opposite ends is in direct fluidic communication with the first channel section and the outlet, and includes an optically clear channel subsection, or is completely optically clear; the third channel section at opposite ends is in direct fluidic communication with the first channel section and the inlet; and, the first channel section provides a resistance that is at least 80% and less than 100% of the combined resistance encountered by a fluid traversing the first and second channel sections, and/or of the microfluidic circuit; b) an image recording system optically connected to the optically clear channel section of each of the at least two microfluidic circuits; and, c) a pressure control unit configured to deliver fluid into each of the at least two microfluidic circuits.
In some embodiments, this disclosure relates to methods for determining the viscosity and/or other property of a fluid using such a microfluidic viscometer assembly by determining the velocity at which said fluid is moving through said microfluidic channel. In some embodiments, this disclosure relates to methods for determining the viscosity of a fluid using such a microfluidic viscometer by: a) introducing a fluid into the microfluidic channel; b) capturing at least two images of a fluid-air interface between said fluid and air within the optically clear channel section of said microfluidic channel; c) comparing the at least two images to determine the position of said fluid-air interface in each image; and, d) determining the velocity at which said fluid is moving through said microchannel using the position of said fluid-air interface in each image; and optionally further calculating the shear stress, apparent shear rate, apparent viscosity, true shear rate, true viscosity, and/or other property, of said fluid.
In some embodiments, this disclosure relates to methods for determining the viscosity and/or other property of a fluid using such a microfluidic viscometer assembly by: a) introducing a first fluid into a first inlet to load the fluid into a first channel section of a first microfluidic circuit of a microfluidic cartridge comprising at least two microfluidic circuits, each microfluidic circuit comprising: an inlet; at least one microfluidic channel comprising: a first channel section having a first diameter and an end in direct fluidic communication with the inlet, and, a second channel section having an optically clear channel subsection, or being completely optically clear, and having a second diameter greater than the first diameter, wherein the second channel section is in direct fluidic communication with the first channel section at an end opposite the inlet, and, an outlet in fluid communication with the second channel section at an end opposite the first channel section, wherein the first channel section provides a resistance to a fluid traversing said microfluidic channel that is at least 80% and less than 100% of a combined resistance of the first and second channel sections, and/or of the microfluidic circuits; b) applying a constant pressure or a preset change in pressure over time, to said first channel section to move the fluid from the first channel section to the second channel section; c) determining the velocity at which said fluid is moving through said second channel section; and, d) using the velocity to determine the viscosity and/or other property of the first fluid.
In some embodiments, this disclosure relates to method for determining the viscosity of a fluid using such a microfluidic viscometer assembly by: a) introducing a first fluid into a first inlet to load the fluid into a microfluidic channel of a first microfluidic circuit of a microfluidic cartridge comprising at least two microfluidic circuits, each microfluidic circuit comprising: an inlet; an outlet; at least one microfluidic channel comprising at least a first, second and third channel section, wherein: the first channel section is positioned between the second and third channel sections; the second channel section at opposite ends is in direct fluidic communication with the first channel section and the outlet, and includes an optically clear channel subsection, or is completely optically clear; the third channel section at opposite ends is in direct fluidic communication with the first channel section and the inlet; and, the first channel section provides a resistance that is at least 80% and less than 100% of the combined resistance encountered by a fluid traversing the first and second channel sections, or of the microfluidic circuit; b) applying a constant pressure or a preset change in pressure over time, to said first channel section to move the fluid from the first channel section to the second channel section; c) determining the velocity at which said fluid is moving through said second channel section; and, d) using the velocity to determine the viscosity and/or other property of the first fluid.
In some embodiments, this disclosure relates to methods for determining the viscoelasticity of a fluid, said method comprising: a) introducing a first fluid into a first inlet to load the fluid into a first channel section, second channel section, and third channel section of a first microfluidic channel to create a first fluid-air interface in the second channel section, wherein the first microfluidic channel is part of a first microfluidic circuit of a microfluidic cartridge comprising at least two microfluidic circuits, each microfluidic circuit comprising: i) an inlet; ii) an outlet; iii) at least one microfluidic channel comprising at least a first, second and third channel section, wherein: the first channel section is positioned between the second and third channel sections; the second channel section at opposite ends is in direct fluidic communication with the first channel section and the outlet, and includes an optically clear channel subsection, or is completely optically clear; the third channel section at opposite ends is in direct fluidic communication with the first channel section and the inlet; and, the first channel section provides a resistance that is at least 80% and less than 100% of the combined resistance encountered by a fluid traversing the first and second channel sections, or of the microfluidic circuit; b) applying a positive pressure followed by a negative pressure to the first inlet to produce a pressure profile in the shape of a sine wave to the first microfluidic channel, thereby producing an oscillatory flow within the second channel section thereof; c) tracking movement of the fluid within the second channel section of the first microfluidic channel to generate a response sine curve; and, d) determining the viscoelasticity of the first fluid by comparing the response sine curve to the pressure profile.
In some embodiments, this disclosure relates to methods for determining the density of a fluid, said method comprising: a) introducing the fluid into a first sample reservoir to load the fluid, which can also be referred to herein as the fluid sample or the sample fluid, into a first inlet via a fluidic connection connecting the first sample reservoir to the first inlet, thereby loading the fluid into a first channel section of a first microfluidic circuit of a microfluidic cartridge comprising at least two microfluidic circuits, each microfluidic circuit comprising: i) an inlet; ii) at least one microfluidic channel comprising: a first channel section having a first diameter and an end in direct fluidic communication with the inlet, a second channel section having an optically clear channel subsection, or being completely optically clear, and having a second diameter greater than the first diameter, wherein the second channel section is in direct fluidic communication with the first channel section at an end opposite the inlet, and an outlet in fluid communication with the second channel section at an end opposite the first channel section, wherein the first channel section provides a resistance to a fluid traversing said microfluidic channel that is at least 80% and less than 100% of a combined resistance of the first and second channel sections, and/or of the microfluidic circuits; b) continuing to load the fluid from the first sample reservoir into the microfluidic circuit to move the fluid from said first channel section of the first microfluidic circuit to the second channel section; c) applying a constant pressure to the second channel section through the output; d) determining the velocity at which said fluid is moving through said second channel section of the first microfluidic circuit; and, e) using the velocity to determine the density of the fluid. In some embodiments, the velocity determination is used to determine when the fluid stops moving, and the density of the fluid is determined by measuring the pressure when the fluid stops moving.
In some embodiments, this disclosure relates to product(s) comprising at least one, and in illustrative embodiments at least two microfluidic viscometer microfluidic cartridges, each microfluidic cartridge comprising at least one microfluidic circuit through which said fluid can flow, each microfluidic circuit comprising: an inlet through which said fluid can be loaded into the microfluidic circuit; a microfluidic channel comprising a first channel section having a first diameter, and a second optically clear channel section having a second diameter greater than the first diameter, wherein the walls of the first channel section and the second channel section are comprised of the same or different non-deformable composition, and wherein the first channel section provides a resistance that is at least 80% (and in some embodiments at least 85%, 90%, or 95% of the resistance) and less than 100% of a combined resistance of the first and second channel sections; and, an outlet through which said fluid can exit the channel. In some embodiments, this disclosure relates to product(s) comprising at least one, and in illustrative embodiments, at least two microfluidic viscometer microfluidic cartridges, each microfluidic cartridge comprising: at least one microfluidic circuit through which said fluid can flow, each microfluidic circuit comprising: an inlet through which said fluid can be loaded into the microfluidic circuit; a microfluidic channel comprising a first channel section having a first diameter, a second channel section having a second diameter greater than the first diameter, a third optically clear channel section having a third diameter greater than the first diameter and optionally the same as the second diameter, wherein the first channel section provides a resistance that is at least 80% (and in some embodiments at least 85%, 90%, or 95% of the resistance) and less than 100% of a combined resistance of the first, second and third channel sections, and wherein the walls of the first, second and third channel sections comprise the same or different non-deformable composition; and, an outlet through which said fluid can exit the channel. In some such embodiments, the product(s) can further include a computer program stored on a computer memory, wherein the computer program comprises instructions for performing an image analysis function to determine velocity of a fluid through each of the microfluidic circuits and to use said velocity to determine a viscosity of the fluid, optionally wherein the image analysis function is a computer program stored on a remote computer server. Each cartridge provided herein, can be a plastic and in illustrative embodiments, disposable cartridge, and each cartridge can itself represent a separate embodiment.
In some subembodiments of any embodiment herein, the microfluidic viscometer assembly does not comprise a glass capillary in fluid communication with the microfluidic circuits and/or microfluidic channels.
Other embodiments are also contemplated and may be derived from this disclosure, as will be understood by those of ordinary skill in the art.
This disclosure relates to microfluidic viscometers and assemblies comprising the same that can be used to determine the viscosity and/or other properties of a fluid. The microfluidic viscometer in illustrative embodiments is part of a microfluidic viscometer assembly that comprises a microfluidic cartridge that comprises at least one, and in illustrative embodiments at least two microfluidic circuits comprising at least one microfluidic channel through which the fluid being tested may flow, a pressure controller for regulating the pressure applied to the fluid as it traverses the at least one microfluidic channel, and an imaging device for tracking movement of the fluid through the at least one microfluidic channel for determining the viscosity and/or other properties of the fluid. In some embodiments, the microfluidic channel comprises multiple channel sections or sections where at least a first channel section provides a higher resistance to flow of the fluid through that section than at least one second channel section(s) that provides less resistance to flow of the fluid than the first channel section, where images of the interface between the fluid and air (i.e., the fluid-air interface which may also be understood by those of ordinary skill in the art to be the fluid-air meniscus, and/or the leading visible edge of the fluid as it traverses the microfluidic channel) in the at least one second channel section are obtained and compared over time to determine the viscosity and/or other properties of the fluid. In preferred embodiments, the resistance encountered by a fluid as it traverses the first channel section (i.e., the high-resistance section) of the microfluidic channel accounts for at least 60%, 70%, 75%, 80%, 85%, 90%, 95%, or 98% and less than 100% (and preferably at least 80%, 85%, 90%, or 95%) of the resistance encountered by the fluid as it traverses the microfluidic channel (the first and second channel sections and optionally further sections thereof; and/or as it traverses the microfluidic circuit including the inlet and/or the outlet). In some embodiments, the first and second channel sections are continuous, meaning there are no intervening parts between the two sections and/or that the fluid flows directly from the first channel section into the second channel section without flowing through any other part such as, e.g., a connector. Typically, the microfluidic channel is part of a microfluidic circuit comprising an inlet through which fluid is typically introduced into the microfluidic channel, at least two or three sections of the microfluidic channel where at least one section of such microfluidic channel(s) applies higher resistance upon a fluid moving through it than is applied by at least one other section, and an outlet positioned opposite the inlet relative to the microfluidic channel through which fluid can exit the microfludic channel. In some embodiments, one or more microfluidic circuits are positioned within a microfluidic cartridge that can be inserted into, supported by, used with, and/or removed from the microfluidic viscometer. In some embodiments, the microfluidic viscometer assembly comprises multiple microfluidic channels (or microfluidid circuits and/or cartridge(s)) such that multiple fluid samples can be tested simultaneously (i.e., multiplex sample processing).
An illustrative overview of such a microfluidic viscometer assembly is provided by
“Cartridge 1” with First Channel Architecture
In some embodiments, a microfluidic viscometer assembly provided herein comprises a microfluidic cartridge comprising at least one and typically at least two microfluidic circuits, each comprising at least one microfluidic channel, wherein each microfluidic channel comprises multiple sections including at least one first channel section that provides the majority of the resistance a fluid encounters while traversing said microfluidic channel, and at least one second channel section of lower resistance that is at least partially optically clear (e.g., transparent; an optically-clear subsection; it may also be completely optically clear) such that the movement of the fluid can be monitored visually through the optically clear subsection as it traverses the microfluidic channel (e.g., at a fluid-air interface between the fluid and air in that optically clear section); an image recording system optionally linked to a processor that determines a viscosity of the fluid based on a comparison of the two or more of such images (e.g., digital images); and a pressure control unit configured, operable to, and/or adapted to deliver and push fluid into or through each of the circuit(s), and control pressure of the circuit, in illustrative embodiments, independently for each circuit, and automatically using a computer programmed to control, and connected to the pressure control unit. Thus, in some embodiments, the microfluidic viscometer assembly (e.g., apparatus) can comprise a microfluidic cartridge comprising at least one and, in illustrative embodiments, at least two microfluidic channels (e.g., each being part of a microfluidic circuit) having a first channel section of a first diameter and being fluidly connected to a second channel section comprising at least one optically clear subsection and a second diameter greater than the first diameter. In some embodiments, the first and second channel sections are continuous, meaning there are no intervening parts between the two sections and/or that the fluid flows directly from the first channel section into the second channel section without flowing through any other part such as, e.g., a connector. In these microfluidic channels, the first diameter (that of the first channel section) is sufficiently less than that of the second diameter (that of the second channel section) such that the first channel section provides at least 80% (e.g., at least 90% or at least 95%) of the resistance encountered by the fluid as it traverses the microfluidic channel (e.g., as it flows through the first and second channel sections). An illustrative embodiment of such a microfluidic circuit is provided by
“Cartridge 2” with Alternative Channel Architecture
In some embodiments, a microfluidic viscometer assembly provided herein comprises a microfluidic cartridge comprising at least one and typically at least two microfluidic circuits, each comprising at least one microfluidic channel, wherein each microfluidic channel comprises multiple sections including at least a first higher-resistance and second lower-resistance section as described above, wherein the first channel section provides the majority of the resistance a fluid encounters while traversing said microfluidic channel, and at least a third channel section (also a lower-resistance section), wherein the second and third channel sections are positioned on either side of the first channel section, and where at least one or both of the second and/or third channel sections are at least partially optically clear (e.g., transparent; an optically clear subsection) such that the movement of the fluid can be monitored visually through the optically clear subsection to capture images of the fluid as it traverses the microfluidic channel (e.g., at a fluid-air interface between the fluid and air in that optically clear section); an image recording system optionally linked to a processor that determines a viscosity of the fluid based on a comparison of the two or more of such images (e.g., digital images); and, a pressure control unit configured, operable to, and/or adapted to deliver and push fluid into and through each of the circuit(s), and control pressure of the circuit, in illustrative embodiments, independently for each circuit, and automatically using a computer programmed to control, and connected to the pressure control unit. Thus, some embodiments, the microfluidic viscometer apparatus can comprise a microfluidic cartridge comprising at least one microfluidic channel (e.g., as part of a microfluidic circuit) including a first channel section of a first diameter, and second and third channel sections having diameters greater than that of the first diameter and including at least one optically clear subsection, wherein the first channel section is positioned between the second and third channel sections, and wherein the fluid encounters higher resistance in the first channel section relative to the second and/or third channel sections. In some embodiments, the resistance encountered by the fluid in the first channel section accounts for the majority, and in some embodiments at least 60%, 70%, 75%, 80%, 85%, 90%, 95%, or 98% and less than 100% (preferably at least 80%, 85%, 90%, or 95%) of the resistance encountered as it traverses the microfluidic channel (and/or microfluidic circuit; i.e., including at least the first (1) and second (2B-2) channel sections (or in the case of a “reverse” application the first large channel section (2B-1)) but also, in some embodiments, at least the inlet (3) and in some embodiments also including the outlet (4)). An illustrative embodiment of such a microfluidic circuit is provided by
In some embodiments, the microfluidic viscometer assembly comprises at least one microfluidic circuit comprising at least one microfluidic channel as described herein, and/or a cartridge(s) comprising one or more of the same (in some embodiments, preferably at least two microfluidic circuits), an image recording system optically connected to the optically clear section of a lower-resistance section of the microfluidic channel (e.g., part 2 in
This process is also illustrated in
As discussed briefly above, the microfluidic viscometer assembly can include a cartridge comprising multiple microfluidic channels and/or microfluidic circuits.
As discussed above, the microfluidic channel(s) of the microfluidic viscometer include at least two sections where at least one of those sections, sometimes called herein the “first channel section,” “small section,” “resistance section,” “relatively high resistance section,” or “high resistance section,” provides the majority of the resistance encountered by a fluid as it traverses the microfluidic channel (e.g., the first channel section (1) (“Small section”) of the exemplary microfluidic channel illustrated in
In some embodiments, the microfluidic circuits and microfluidic channels may be prepared from any suitable material such as plastic. In some embodiments, the microfluidic circuit and microfluidic channel can be fabricated using a soft lithography technique. In some embodiments, the cartridges can be injection molded using a suitable plastic. In some embodiments, as illustrated in
The exemplary microfluidic viscometer assemblies illustrated in
The pressure control unit provides a known pressure at the inlet of the cartridge that pushes the fluid through the microfluidic channels at a constant rate. In some embodiments, the pressure control unit comprises a manifold (part 7-1 in
The temperature control unit controls the temperature of the cartridge and/or microfluidic channel and/or microfluidic circuit. Temperature is an important factor that affects the viscosity of the fluid and it is important that the temperature of the fluid remain constant as the fluid is traversing the microfluidic circuit. Suitable temperature control units that can be used in the microfluidic viscometers disclosed herein can include, for instance, the illustrative temperature control unit illustrated in
In some embodiments, the microfluidic viscometer may be encased by, for instance a hard shell or case around some or all of the components. For instance,
This disclosure also relates to methods for using a microfluidic viscometer assembly disclosed herein to determine the viscosity and/or other property of a fluid or a collection of fluids (e.g., using a cartridge comprising multiple microfluidic channels and/or microfluidic circuits (e.g., as illustrated in
An illustrative general method is described above with respect to
In some embodiments, a small volume of a fluid sample is initially loaded into a cartridge containing a microfluidic channel. The volume of fluid sample loaded can be 1-100 ul, 2.5-50 ul, 5-50 ul, 5-25 ul, 5-10 ul, 10-50 ul, or 10-25 ul. Depending on the conditions of the particular method being carried out (e.g., imposed pressure drop and fluid viscosity), two to seven seconds can be provided for the fluid to propagate into the horizontal portion of the capillary and image capture is initiated about five seconds after that point (e.g., about 10 seconds of start-up time is allowed before the velocity calculations are initiated). As discussed above, the user can pre-select a temperature and pressure ramp under which the analysis can proceed. As discussed above and shown in, e.g., illustrative
The position of the fluid in the microfluidic channel is tracked by the image recording and processing system positioned above the cartridge, which records (e.g., video) of fluid movement through the channel. The image recording and processing system detects the fluid-air interface and can apply a Hough transform to the edge of the fluid-air interface to determine the distance the interface has moved over time (i.e., the velocity of the fluid). An imaging algorithm incorporated into the image recording and processing system software can extract two or more images from the video, applies contrast, detect the fluid-air interface, and measure velocity. From the velocity profile, the software automatically calculates shear stress, apparent shear rate, apparent viscosity, true shear rate, and true viscosity. For accurate velocity measurement, the fluid must move approximately 100 pixels, so the true minimum distance is dependent on individual recording device (e.g., camera) specifications. Thus, fluid velocity in the channel can be extrapolated from images (e.g., recorded video data). In some embodiments, two or more images are extracted at known time points, and the distance traveled by the fluid over a set time frame is measured. With a known applied pressure, channel geometry, and fluid velocity, this technology can measure the viscosity of both Newtonian and non-Newtonian fluids. In some embodiments, one or more flowmeters could also or alternatively be used to take measurements downstream of the outlet (e.g., not in the cartridge).
In some embodiments, a fluid sample can be loaded into the part labelled in most embodiments as the outlet (e.g., part 4 in
The viscosity and shear rate for Newtonian and non-Newtonian fluids can be computed by the image data processor, also referred to herein as an image analysis processor, which can be part of the image analysis function, from the data captured (e.g., the velocity by which the fluid traversed the microfluidic channel) using the following non-limiting algorithms described here, among others. Such equations can be used for example, in embodiments, when the higher-resistance section of the microfluidic channel provides at least 80%, and in illustrative embodiments at least 85%, 90%, 95%, 98%, or 99% (preferably at least any of 80%, 85%, 90%, or 95%) of the resistance of the combined resistance of all of the microfluidic channels in a microfluidic circuit of any of the architectures provided herein.
Fluid viscosity of a Newtonian fluid is given by the following equation:
where ΔP is the pressure drop applied by the pressure controller, PL is the Laplace pressure due to the surface tension at the fluid-air interface, Q is the flow rate of the fluid in the channel, and S is the geometric factor of the small channel, which is expressed as
where L is the length of the small microchannel, h is the height of the small microchannel, and w is the width of the small microchannel. This equation for the geometric factor of a rectangular channel only applies if h<<w, as is the case for the small microchannel. The geometric factor for the large channel is negligible compared to that of the small channel, so the total geometric factor for the system can be expressed by the equation above.
The flow rate is calculated as shown below:
Q=vA (3)
where v is the velocity of the fluid traveling through the large channel, and A is the cross-sectional area of the large channel. As described previously, capillary pressure is present when one fluid-air interface exists. For a rectangular channel, capillary pressure is calculated as
where σ refers to the surface tension of the fluid, cos θtop refers to the contact angle of the fluid on the top surface of the channel, cos θbottom refers to the contact angle of the fluid on the bottom surface, cos θleft refers to the contact angle of the fluid on the left wall, and cos θright refers to the contact angle of the fluid on the right wall. With this equation, a positive capillary pressure corresponds to fluid resisting movement through the channel, and a negative capillary pressure corresponds to fluid being pulled through the channel. At higher driving pressures, capillary pressure is considered negligible, however if the capillary pressure accounts for more than 20, 15, 10, 9, 8, 7, 6 or preferably about 5, or 5% of the driving pressure, then it should be accounted for.
When h<<w (h being the height of the small microchannel, and w being the width of the small microchannel), as is the case in the exemplary cartridges described here in (e.g., Cartridge 1 and Cartridge 2), the shear rate of a Newtonian fluid through the channel is given by:
However, for a non-Newtonian fluid, which experiences a variable flow profile through the channel, the true shear rate can be expressed as
where the apparent shear rate is multiplied by the Weissenberg-Rabinowitch correction factor. In Equation (6), τw is dependent on pressure drop and the geometry of the small channel:
Thus, for a non-Newtonian fluid, the viscosity is equal to
To determine the true shear rate for a non-Newtonian fluid using Equation (6), the term d(ln {dot over (γ)}0)/d(ln τw) must first be approximated by plotting apparent shear rate versus shear stress for a range of pressure drops, fitting an appropriate polynomial to the points, and differentiating. Then, the true shear rate, and subsequently the viscosity, can be found for each pressure drop.
The K value can also be calculated (as in the Examples), and represents the geometric factor of the channel, and the expression to find K is [(ΔP+PL)/μ/Q]. Calculating the K value is an indirect method of measuring the geometric factor S described in the patent draft. One can determine K by running fluids of known viscosity through the channel at a known pressure and measuring flow rate.
A more general formula can be utilized for microfluidic channels of shapes other than rectangular/trapezoidal: PL=2γ cos θ/r, where r is the radius for a circular channel, or the effective radius for a channel with a different cross-sectional shape.
As shown in the Examples, these microfluidic viscometers have been used to determine the fluid flow rate of glycerol-based, polyethylene oxide (PEO)-based, and protein-containing (e.g., BSA, monoclonal antibodies) test samples. To do so, 5-10 μL of sample fluid was added to the inlet of the microfluidic circuit, and driven through the microfluidic channel by a constant pressure (the source of pressure being, e.g., a hydrostatic head or OB1 MK3 microfluidic flow control system). As the fluid flowed through the microfluidic circuit, a video capture device was utilized to capture fluid velocity within the microfluidic channel. The collected video was then postprocessed in an image processing device (ImageJ) to determine the fluid flow rate traveling through the microfluidic circuit, and subsequently the fluid viscosity. Each fluid sample run was concurrently measured using a Brookfield AMETEK DV2T Viscometer, and found to accurately correspond to the results with that machine. A number of functions discussed herein can be implemented on a computing device by software, firmware, hardware, or a combination thereof as part of a computer system. All or part of the computing device and other components of the computer system can be, but are not required to be, physically associated with other components of a viscometer provided herein. The computer system can be a physically separate computer system from the viscometer, for example a personal computer or a terminal for accessing the Internet. These functions can be implemented as computer-readable code on a single computer system, or on multiple computer systems, which can perform and process various tasks. These functions can include, for example, video and/or image capture, storage and loading, as well as identifying, enhancing, and measuring objects in a video and/or an image, such as a fluid-air interface in a channel, and other processing functions of the image data processor, also referred to herein as an image analysis processor. Furthermore, the functions can include data analysis functions for determining velocity of a fluid through a microfluidic channel and/or to determine viscosity from this velocity, by performing the mathematical equations provided herein on data captured from the capture images. Plots can be generated by a computing device associated with a viscometer, such as those plotting viscosity over a time or temperature range. In addition, the functions can include functions to provide a graphical user interface to communicate with a user and allow user input, and for processing date input thru the graphical user interface for example to provide control, including automatic control, of various parts of the viscometer, such as a pressure control unit and/or a temperature control unit.
A user can input an identifying characteristic of a cartridge provided herein, such as a lot number or catalog number. In certain embodiments, a device associated with a viscometer provided herein, can read a barcode or RFID or other identifying object associated with a cartridge that is loaded onto a viscometer provided herein. This information can then be input into a computing device associated with the viscometer and used to capture information about the cartridge for example from a storage device associated with an Internet server, such as the number of microfluidic circuits on the cartridge and/or whether the cartridge has already been used to perform a method and/or which circuits on a cartridge have not been used to perform a method. Furthermore, an interface can allow a user to enter information about a sample loaded into a cartridge and/or other information such as date or lot number of a fluid being tested.
Processing tasks can be carried out by one or more processors. However, it should be noted that various types of processing technology may be used here, including programmable logic arrays (PLAs), application-specific integrated circuits (ASICs), multi-core processors, multiple processors, or distributed processors. Additional specialized processing resources such as graphics, multimedia, or mathematical processing capabilities may also be used to aid in certain processing tasks. These processing resources may be hardware, software, or an appropriate combination thereof. For example, one or more of processors may be a graphics-processing unit (GPU).
Computer system also includes a main memory and may also include a secondary memory. Main memory may be a volatile memory or non-volatile memory and divided into channels. Memory may be associated with an internet server and said computer system could include a computer terminal connected over a local or wide area network such as the Internet, to a server. Secondary memory may include, for example, non-volatile memory such as a hard disk drive, a removable storage drive, and/or a memory stick. Removable storage drive may comprise a floppy disk drive, a magnetic tape drive, an optical disk drive, a flash memory, or the like. The removable storage drive reads from and/or writes to a removable storage unit in a well-known manner. Removable storage unit may comprise a floppy disk, magnetic tape, optical disk, etc. which is read by and written to by removable storage drive. As will be appreciated by persons skilled in the relevant art(s), removable storage unit includes a computer usable storage medium having stored therein computer software and/or data.
Computer system may also include a communications and network interface. Communication and network interface allows software and data to be transferred between computer system and external devices and/or between a computer system physically associated with a viscometer and a computer system not associate with the viscometer, such as an Internet server. Communications and network interface may include a modem, a communications port, a PCMCIA slot and card, or the like. Software and data transferred via communications and network interface are in the form of signals which may be electronic, electromagnetic, optical, or other signals capable of being received by communication and network interface. These signals are provided to communication and network interface via a communication path. Communication path carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, blue tooth, WI-FI, an RF link or other communications channels.
A communication and network interface can be associated with the computer system and allows a computer system associated with the viscometer to communicate over communication networks or mediums such as LANs, WANs the Internet, etc. The communication and network interface may interface with remote sites or networks via wired or wireless connections.
Instructions for performing functions discussed herein for operating a viscometer and determining viscosity, can be encoded as computer-readable code on a computer program medium. In this document, the terms “computer program medium,” “computer-usable medium” and “non-transitory medium” are used to generally refer to tangible media such as removable storage unit, removable storage drive, and a hard disk installed in hard disk drive, including a hard drive connected to a server. Signals carried over communication path can also embody the logic described herein. Computer program medium and computer usable medium can also refer to memories, such as main memory and secondary memory, which can be memory semiconductors (e.g. DRAMs, etc.). These computer program products are means for providing software to the computer system.
Computer programs (also called computer control logic) are stored in main memory and/or secondary memory. Computer programs may also be received via communication and network interface. Such computer programs, when executed, enable the computer system to implement viscometer control and viscosity determination functions as discussed herein. In particular, the computer programs, when executed, enable processor to implement the disclosed processes. Accordingly, such computer programs represent controllers of the computer system. Where the embodiments are implemented using software, the software may be stored in a computer program product and loaded into computer system using removable storage drive, interfaces, hard drive or communication and network interface, for example.
The computer system may also include input/output/display device, such as keyboards, monitors, pointing devices, touchscreens, etc. Such input/output/display device can be physically associated with a viscometer disclosed herein, or can be physically separate.
The embodiments are also directed to computer program products comprising software stored on any computer-usable medium. Such software, when executed in one or more data processing devices, causes a data processing device(s) to operate as described herein. Embodiments employ any computer-usable or -readable medium, and any computer-usable or -readable storage medium known now or in the future. Examples of computer-usable or computer-readable mediums include, but are not limited to, primary storage devices (e.g., any type of random access memory), secondary storage devices (e.g., hard drives, floppy disks, CD ROMS, ZIP disks, tapes, magnetic storage devices, optical storage devices, MEMS, nano-technological storage devices, etc.), and communication mediums (e.g., wired and wireless communications networks, local area networks, wide area networks, intranets, etc.). Computer-usable or computer-readable mediums can include any form of transitory (which include signals) or non-transitory media (which exclude signals). Non-transitory media comprise, by way of non-limiting example, the aforementioned physical storage devices (e.g., primary and secondary storage devices).
In some aspects, a microfluidic viscometer assembly provided herein can be used to determine the viscoelasticity of a fluid. Most fluids display both viscous and elastic properties. By creating an oscillatory fluid flow, one can determine the elastic modulus (G′) and the loss modulus (G″) to assess the viscoelasticity of the fluid. Conventionally, this is done in a rotational rheometer, where a test is performed in the form of a sine curve, with the fluid being sheared back and forth, and the phase shift between the preset sine curve and the response sine curve (the fluid motion) is found. In one aspect, provided herein is a method for using a microfluidic viscometer assembly provided here, to produce oscillatory flow by applying an oscillating field to the fluid in the channels and tracking the movement of the interface in the large channel. In illustrative embodiments, such a method is performed in Cartridge 2 disclosed herein (e.g., as illustrated in
In this aspect for determining a viscoelasticity, after the fluid is introduced into the microfluidic channel via the first inlet, a positive pressure followed by a negative pressure is applied to the inlet to produce a pressure profile in the shape of a sine wave to the microfluidic channel, thereby producing an oscillatory flow within the second channel section thereof. The pressure control unit herein can be controlled and programmed using a computer interface as provided herein, to perform this positive and negative pressure cycling. Then movement of the fluid within the second channel section of the microfluidic channel is observed, visualized, recorded, and/or tracked to generate a response sine curve. This function is typically carried out by the image recording system provided herein. Viscoelasticity of the first fluid can then be determined (typically calculated and/or measured) by comparing the response sine curve to the pressure profile. Mathematical equations and analysis for performing such comparison can be performed using methods and equations known in the art for viscoelasticity determinations. One or more computer systems that are physically connected to, or separate from, a microfluidic viscometer provide herein, can be programmed to accept user input to request a viscoelasticity determination, to control the pressure unit to create the pressure profile in the shape of a sine wave, and to analyze images and/or video captured by the image recording system and to analyze and compare data. Thus, the one or more computer systems in such embodiments are digitally connected to a user interface, the pressure control unit, and the image recording system to perform these functions. As will be understood, virtually any of the embodiments of the microfluidic viscometer assembly provided herein for viscosity determination can be used for and/or applied to viscoelasticity determination.
Accordingly, provided herein in one aspect is a method for determining the viscoelasticity of a fluid, that includes: a) introducing a first fluid into a first inlet to load the fluid into a first channel section, second channel section, and third channel section of a first microfluidic channel to create a first fluid-air interface in the second channel section, wherein in illustrative embodiments, the first microfluidic channel is part of a first microfluidic circuit of a microfluidic cartridge comprising at least two microfluidic circuits, each microfluidic circuit comprising: i) an inlet; ii) an outlet; iii) at least one microfluidic channel comprising at least a first, second and third channel section, wherein: the first channel section is positioned between the second and third channel sections; the second channel section at opposite ends is in direct fluidic communication with the first channel section and the outlet, and comprises an optically clear channel subsection, or is completely optically clear; the third channel section at opposite ends is in direct fluidic communication with the first channel section and the inlet and optionally comprises an optically clear channel subsection, or is completely optically clear; and, the first channel section provides a resistance that is at least 80% and less than 100% of the combined resistance encountered by a fluid traversing the first and second channel sections, or of the microfluidic circuit; b) applying a positive pressure followed by a negative pressure to the first inlet to produce a pressure profile in the shape of a sine wave to the first microfluidic channel, thereby producing an oscillatory flow within the second channel section thereof; c) tracking movement of the fluid within the second channel section of the first microfluidic channel to generate a response sine curve; and, d) determining the viscoelasticity of the first fluid by comparing the response sine curve to the pressure profile. In some embodiments, there is a fluid-air interface in both the second channel section and third channel section, and the response curve could be found by imaging either interface.
In some aspects, a microfluidic viscometer assembly provided herein can be used to determine the density of a fluid. Such an application for density determination is illustrated in
This hydrostatic pressure (ΔP) generated from the flow of fluid from the reservoir into the microfluidic circuit is equal to the density of the sample fluid (p) multiplied by the acceleration due to gravity (g) and the vertical distance between the top of the sample fluid in the reservoir and the cartridge (h): ΔP=ρgh. Thus, the hydrostatic pressure is unknown, because density is unknown. At the same time, a pressure controller will apply a constant pressure at the outlet (244). When the pressure from the controller equals the hydrostatic pressure, the fluid will remain stationary. Therefore, the image recording system (e.g. camera) can track the movement of the interface, and the pressure applied at the outlet can be adjusted until fluid movement stops. At this point, the hydrostatic pressure will be known and the density can be determined (back-calculated). A computer system can be connected to and can control the various functional units of a microfluidic viscometer herein to perform such a method of density determination.
Accordingly, provided herein in one embodiment is a method for determining the density of a fluid, the method comprising: a) introducing the fluid into a first sample reservoir to load the fluid sample into a first inlet via a fluidic connection connecting the first sample reservoir to the first inlet, thereby loading the fluid into a first channel section of a first microfluidic circuit of a microfluidic cartridge comprising at least two microfluidic circuits, each microfluidic circuit comprising: i) an inlet; ii) at least one microfluidic channel comprising: a first channel section having a first diameter and an end in direct fluidic communication with the inlet, a second channel section having an optically clear channel subsection, or being completely optically clear, and having a second diameter greater than the first diameter, wherein the second channel section is in direct fluidic communication with the first channel section at an end opposite the inlet, and an outlet in fluid communication with the second channel section at an end opposite the first channel section, wherein the first channel section provides a resistance to a fluid traversing said microfluidic channel that is at least 80% and less than 100% of a combined resistance of the first and second channel sections, and/or of the microfluidic circuits; b) continuing to load the fluid from the sample reservoir into the microfluidic circuit to move the fluid from said first channel section of the first microfludic circuit to the second channel section; c) applying a constant pressure to the second channel section through the output; d) determining the velocity at which said fluid is moving through said second channel section of the first microfluidic circuit; and, e) using the velocity to determine the density of the fluid. In another embodiment is a method for determining the density of a fluid, the method comprising: a) introducing the fluid into a first sample reservoir to load the fluid sample into a first inlet via a fluidic connection connecting the first sample reservoir to the first inlet, thereby loading the fluid into a first channel section of a first microfluidic circuit of a microfluidic cartridge comprising at least two microfluidic circuits, each microfluidic circuit comprising: i) an inlet; ii) at least one microfluidic channel comprising at least a first, second and third channel section, wherein: the first channel section is positioned between the second and third channel sections; the second channel section is in direct fluidic communication with the first channel section and the outlet, and includes an optically clear channel subsection, or is completely optically clear; the third channel section is in direct fluidic communication with the first channel section and the inlet, wherein the first channel section provides a resistance to a fluid traversing said microfluidic channel that is at least 80% and less than 100% of a combined resistance of the first and second channel sections, and/or of the microfluidic circuits; b) continuing to load the fluid from the sample reservoir into the microfluidic circuit to move the fluid from said first channel section of the first microfluidic circuit to the second channel section; c) applying a constant pressure to the second channel section through the output; d) determining the velocity at which said fluid is moving through said second channel section of the first microfluidic circuit; and, e) using the velocity to determine the density of the fluid. In illustrative embodiments, the velocity determination is used to determine when the fluid stops moving, and the density of the fluid is determined by measuring the pressure when the fluid stops moving.
While the microfluidic viscometers disclosed herein may be used to determine viscosity and/or density of a fluid, these may also be used to measure hydrodynamic radius, intrinsic viscosity, extensional viscosity (e.g., uniaxial), to produce a protein denaturation curve, to determine protein conformation, to conduct an injectability determination, molecular weight determination, conduct a shear rate and/or temperature sweep, and/or conduct stability and/or quality, or quality control tests. For instance, the hydrodynamic radius of a protein can be found from the Einstein viscosity relation [η]=2.5NVe/M, where [η] is the intrinsic viscosity, N is Avogadro's number, Ve is the effective volume of one protein molecule modeled as a sphere, and M is the molecular weight of the protein. If the intrinsic viscosity and molecular weight of the protein are known, the effective volume can be determined, and the hydrodynamic radius can be found using the volume equation for a sphere. (Armstrong J K, Wenby R B, Meiselman H J, Fisher T C. The hydrodynamic radii of macromolecules and their effect on red blood cell aggregation. Biophys J. 2004; 87(6):4259-70.) The intrinsic viscosity can be found by first finding the specific viscosity (ηsp), which is equal to (η−η0)/η0, where η is the viscosity of the solution, and η0 is the viscosity of the solvent. A solution's intrinsic viscosity can be found by plotting the specific viscosity divided by the concentration of the solution at several concentrations and extrapolating the viscosity at a concentration of zero. (Armstrong J K, Wenby R B, Meiselman H J, Fisher T C. The hydrodynamic radii of macromolecules and their effect on red blood cell aggregation. Biophys J. 2004; 87(6):4259-70.) Uniaxial extensional viscosity of a Newtonian fluid is equal to three times the shear viscosity, and thus can be found by measuring the viscosity of a fluid sample and multiplying the value by three. A protein denaturation curve can be produced by measuring viscosity across a range of temperatures and determining a temperature at which there is a clear change in the viscosity curve. Protein conformation can be determined from the Mark-Houwink equation above, by finding the value for the constant ‘a’ from intrinsic viscosity and molecular weight. For compact, sphere-shaped molecules a=0, for random coiled molecules, a is between 0.5 and 0.8, and for rod-shaped molecules a=1.8. (Sousa, Isabel & Mitchell, John & Hill, Sandra & Harding, Stephen. (1995). Intrinsic viscosity and Mark-Houwink parameter of lupin proteins in aqueous solutions. Les Cahiers de rheologie. 14. 139-148.) Information on injectability can be determined by measuring the viscosity of injectable solutions at relevant shear rates to determine if appropriate concentrations of active solution can be safely delivered into the body. The molecular weight of a protein can be determined from its intrinsic viscosity by employing the Mark-Houwink equation [η]=KMa where K and a are constants that depend on the specific protein and solvent. (Sousa, Isabel & Mitchell, John & Hill, Sandra & Harding, Stephen. (1995). Intrinsic viscosity and Mark-Houwink parameter of lupin proteins in aqueous solutions. Les Cahiers de rheologie. 14. 139-148.) To conduct a shear rate and/or temperature sweep, the viscosity of a fluid sample can be measured across a range of temperatures or pressures to understand how the fluid is affected. The stability and/or quality of a fluid can be evaluated by determining whether the protein denatures at certain relevant temperatures and by measuring the viscosity at various time points to understand how the protein solution behaves over time. Other techniques may also be suitable as may be determined by those of ordinary skill in the art.
Exemplary fluids that can be tested using the microfluidic viscometers disclosed herein can include but are not limited to protein solutions, biological samples (e.g., blood, synovial fluid, saliva, vitreous humor), foods (e.g., ketchup, mustard), cosmetics (e.g., creams such as shaving cream, lotions), pharmaceutical formulations, paints (e.g., colloidal suspensions admixed with polymers), inks, oils (e.g., engine oil), thickeners, petroleum products. It is understood in the art that each of these types of fluids exhibit different shear rates (e.g., 10−6 to 107 1/s) and viscosities of, e.g., from about 10−4 to 108 Pa·s (e.g., most biological fluids being between 10−4 to 103 (see, e.g., Gupta, Biomicrofluids 10, 043402 (2016)). In general, the microfluidic viscometers disclosed herein can be used to study Newtonian and non-Newtonian viscous and/or viscoelastic fluids having shear rates of from about 1 to about 500,000 1/s and/or viscosities of from about 0.1 to about 50,000 Pascals (Pas).
In some embodiments, then, this disclosure provides a microfluidic viscometer assembly, the assembly comprising: a) a microfluidic cartridge comprising at least two microfluidic circuits, each microfluidic circuit comprising: i) an inlet; ii) at least one microfluidic channel comprising: a first channel section having a first diameter and an end in direct fluidic communication with the inlet, and, a second channel section having an optically clear channel subsection, or being completely optically clear, and having a second diameter greater than the first diameter, wherein the second section is in direct fluidic communication with the first section at an end opposite the inlet; and, iii) an outlet in fluid communication with the second channel section at an end opposite the first channel section, wherein the first channel section provides a resistance to a fluid traversing said microfluidic channel that is at least 80% and less than 100% of a combined resistance of the first and second channel sections, and/or of the microfluidic circuits; b) an image recording system optically connected to the optically clear channel section of the at least two microfluidic circuits; and, c) a pressure control unit. And in some embodiments, this disclosure provides a microfluidic viscometer assembly, the assembly comprising: a) a microfluidic cartridge comprising at least two microfluidic circuits, each microfluidic circuit comprising a microfluidic channel comprising: i) an inlet; ii) an outlet; iii) at least one microfluidic channel comprising at least a first, second and third channel section, wherein the first channel section is positioned between the second and third channel sections; the second channel section is in direct fluidic communication with the first channel section and the outlet, and includes an optically clear channel subsection, or is completely optically clear; the third channel section is in direct fluidic communication with the inlet; and, the first channel section provides a resistance that is at least 80% and less than 100% of the combined resistance encountered by a fluid traversing the first and second channel sections, or of the microfluidic circuits; and, an outlet in fluid communication with the second channel section at an end opposite the first channel section, wherein the first channel section provides a resistance that is at least 80% and less than 100% of a combined resistance of the first channel section and the second channel section; b) an image recording system optically connected to the optically clear channel section of the at least two microfluidic circuits; and, c) a pressure control unit.
Within this disclosure, the first channel section is considered the higher-resistance section and the second channel section is considered to be a lower-resistance section. As explained above, the widths and/or heights are important to the function of each as a high-resistance or low-resistance section. For instance, as indicated above and shown in the Examples below, the h/w ratio for the high-resistance section can be under 0.1, such as about 0.06. In some embodiments, the first channel section provides at least 90% and less than 100%, optionally wherein the first section provides at least 95% and less than 100% of the combined resistance of the first and second channel sections, and/or of the entire microfluidic circuit, for a fluid traversing the microfluidic circuit. In some embodiments, the first and second channel sections are directly fluidly connected without any intervening sections and/or parts. In some embodiments, the first and second channel sections form a straight fluidic flow path without a bend. In some embodiments, the microfluidic viscometer assembly does not comprise a glass capillary in fluid communication with the microfluidic circuits and/or microfluidic channels. It is also noted that, in some embodiments, a fluid may enter or exit the microfluidic circuit by either the inlet or the outlet (e.g., as in the “reverse” method described above).
In some embodiments, the microfluidic viscometer assembly can include a light source, optionally a diffuse light source, optically connected to the optically clear sections of the microfluidic channel. In some embodiments, a single image recording system is positioned above all the microfluidic circuits, or a separate image recording system is positioned above each microfluidic circuit, which can also be referred to as a microfluidic channel circuit. In some embodiments, the microfluidic viscometer assembly further includes an image analysis function comprising an image analysis processor comprising instructions to determine velocity of a fluid through each of the microfluidic circuits and to use said velocity to determine a viscosity of the fluid, optionally wherein the image analysis function is a computer program stored on a memory of a computer that is not physically associated with, or connect to the image recording system, or optionally any other physical component of the microfluidic viscometer assembly. In some embodiments, the image analysis function is an automatic function because it is preprogrammed to run the program without further user intervention. In some embodiments, the image analysis function further comprises instructions to calculate shear stress, apparent shear rate, apparent viscosity, true shear rate, and/or true viscosity of said fluid of a fluid in each of the microfluidic circuits.
In some embodiments, each microfluidic cartridge can include four to 36 of said microfluidic circuits, and optionally comprises 10 or 12 microfluidic circuits. In some embodiments, the microfluidic cartridge is a disposable microfluidic cartridge, removably connected to a microfluidic instrument comprising the image recording system and pressure control unit. In some embodiments, the microfluidic circuits of the microfluidic cartridge are formed in plastic that may be non-deformable. In some embodiments, the walls of the first channel section and the second channel section are non-deformable, and have the same or different composition.
In some embodiments, this disclosure provides methods for determining the viscosity of a fluid using a microfluidic viscometer assembly disclosed herein, the method including determining the velocity at which said fluid is moving through said microchannel. In some embodiments, such methods include: a) introducing a fluid into the microfluidic channel; b) capturing at least two images of a fluid-air interface between said fluid and air within the optically clear channel section of said microfluidic channel; c) comparing the at least two images to determine the position of said fluid-air interface in each image; and, d) determining the velocity at which said fluid is moving through said microchannel using the position of said fluid-air interface in each image; and optionally further calculating the shear stress, apparent shear rate, apparent viscosity, true shear rate, and/or true viscosity of said fluid.
In some embodiments, the methods include: introducing a first fluid into a first inlet to load the fluid into a first channel section of a first microfluidic circuit of a microfluidic cartridge comprising at least two microfluidic circuits, each microfluidic circuit comprising: i) an inlet; ii) at least one microfluidic channel comprising a first channel section having a first diameter and an end in direct fluidic communication with the inlet, and a second channel section having an optically clear channel subsection, or being completely optically clear, and having a second diameter greater than the first diameter, wherein the second channel section is in direct fluidic communication with the first channel section at an end opposite the inlet; and, iii) an outlet in fluid communication with the second channel section at an end opposite the first channel section; wherein the first channel section provides a resistance to a fluid traversing said microfluidic channel that is at least 80% and less than 100% of a combined resistance of the first and second channel sections, and/or of the microfluidic circuits; applying a constant pressure to said first channel of the first channel circuit to move the fluid from the first channel section to the second channel section of the microfluidic circuit; determining the velocity at which said fluid is moving through said second channel section; and, using the velocity to determine the viscosity of the first fluid.
In some embodiments, such methods include: a) introducing a first fluid into a first inlet to load the fluid into a first channel section of a first microfluidic circuit of a microfluidic cartridge comprising at least two microfluidic circuits, each microfluidic circuit comprising: i) an inlet; ii) an outlet; iii) at least one microfluidic channel comprising at least a first, second and third channel section, wherein: the first channel section is positioned between the second and third channel sections; the second channel section is in direct fluidic communication with the first channel section and the outlet, and includes an optically clear channel subsection, or is completely optically clear; the third channel section is in direct fluidic communication with the inlet; and, the first channel section provides a resistance that is at least 80% and less than 100% of the combined resistance encountered by a fluid traversing the first and second channel sections, or of the microfluidic circuits; and, the outlet is in fluid communication with the second channel section at an end of the microfluidic circuit opposite the first channel section, and wherein the first channel section provides a resistance that is at least 80% and less than 100% of a combined resistance of the first channel section and the second channel section; b) applying a constant pressure to said first channel of the first channel circuit to move the fluid from the first channel section to the second channel section of the first channel circuit; c) determining the velocity at which said fluid is moving through the second channel section; and, using the velocity to determine the viscosity of the first fluid.
In some embodiments, the method include removably connecting a microfluidic cartridge as disclosed herein to a microfluidic viscometer comprising: a pressure control unit, wherein the pressure control unit applies the constant pressure to said first channel section; and, an image recording system, wherein the image recording system captures images that are used to determine the velocity at which said fluid is moving through said second channel section. In some such embodiments, said microfluidic cartridge comprises microfluidic circuits comprising microfluidic channels including a least one section (e.g., the above-described first channel section) having a height less than 0.1 its width.
In some embodiments, the microfluidic viscometer and methods of use comprise and/or can be used to study Newtonian and/or non-Newtonian fluids. In some embodiments, the fluid is an aqueous fluid, an oil-based fluid is not loaded into a microchannel, and/or an oil-aqueous fluid interface is not formed. In some embodiments, the viscosity of multiple fluid samples of such fluids, the same or different, are determined simultaneously. In some embodiments, a control fluid is not loaded into a microfluidic circuit during the method. In some embodiments, the velocity of a fluid is determined by extracting two or more images recorded by the image recording system, and comparing a fluid-air interface in each of said images. In some embodiments in which the microfluidic viscometer assembly further comprises a diffuse light source, and the method further comprises illuminating the optically clear channel section to enhance detection of the fluid-air interface. In some embodies, the methods include removing the microfluidic cartridge from the instrument after determining the viscosity of a first fluid. In some embodiments, the methods further include removably connecting another microfluidic cartridge to the instrument and repeating the method to determine the viscosity of a second fluid. In some embodiments, the method is first performed to determine the viscosity of at least two different fluids loaded into different microfluidic circuits of the microfluidic cartridge, and then is performed on at least two additional fluids loaded into the other microfluidic cartridge. In some embodiments, in addition to velocity, viscosity is determined using the pressure and dimensions of the first channel section, the second channel section, and optionally the third channel section, of the microfluidic channel.
In some embodiments, this disclosure provides a product(s) comprising at least two microfluidic viscometer microfluidic cartridges, each microfluidic cartridge comprising at least one microfluidic circuit through which said fluid can flow, each microfluidic circuit comprising: an inlet through which said fluid can be loaded into the channel, a first channel section having a first diameter, and second optically clear channel section having a second diameter greater than the first diameter, wherein the walls of the first channel section and the second channel section are comprised of the same or different non-deformable composition and wherein the first channel section provides a resistance that is at least 80% and less than 100% of a combined resistance of the first channel section and the second channel section; and, an outlet through which said fluid can exit the channel. In some embodiments, such product can include at least two microfluidic viscometer microfluidic cartridges, each microfluidic cartridge comprising: at least one microfluidic circuit through which said fluid can flow, each microfluidic circuit comprising an inlet through which said fluid can be loaded into the microfluidic circuit; at least one microfluidic channel comprising a first channel section having a first diameter, a second and/or third channel section having a second diameter greater than the first diameter and optically clear subsection (or is completely optically clear) with diameter(s) greater than the first diameter and optionally the same as one another (i.e., the second and third channel sections have the same diameter), wherein the first channel section provides a resistance that is at least 80% and less than 100% of a combined resistance of the first, second and third channel sections, and wherein the walls of the first, second and third channel sections comprise the same or different non-deformable composition; and, an outlet through which said fluid can exit the channel. In some embodiments, the product further comprises a computer program stored on a computer memory, wherein the computer program comprises instructions for performing an image analysis function to determine velocity of a fluid through each of the microfluidic circuits and to use said velocity to determine a viscosity of the fluid, optionally wherein the image analysis function is a computer program stored on a memory of a remote computer server. In some embodiments, the computer program is accessible over the Internet or stored on a storage device. In some embodiments, the product further comprises instructions for loading the microfluidic viscometer microfluidic cartridges into a microfluidic viscometer. Other embodiments are also contemplated by this disclosure, as may be determined by one of ordinary skill in the art.
The terms “about”, “approximately”, and the like, when preceding a list of numerical values or range, refer to each individual value in the list or range independently as if each individual value in the list or range was immediately preceded by that term. The terms mean that the values to which the same refer are exactly, close to, or similar thereto.
Optional or optionally means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event or circumstance occurs and instances where it does not. For example, the phrase optionally the composition can comprise a combination means that the composition may comprise a combination of different molecules or may not include a combination such that the description includes both the combination and the absence of the combination (i.e., individual members of the combination).
Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent about or approximately, it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. Ranges (e.g., 90-100%) are meant to include the range per se as well as each independent value within the range as if each value was individually listed.
All references cited within this disclosure are hereby incorporated by reference in their entirety. Certain embodiments are further described in the following examples. These embodiments are provided as examples only and are not intended to limit the scope of the claims in any way.
The examples demonstrate that the microfluidic viscometers described herein are capable of highly accurate, reproducible, low volume (e.g. 10 μL), and multiplexed viscosity measurements of both Newtonian and Non-Newtonian fluids. For instance, glycerol solutions and a model protein solution (BSA) ranging in concentration from 10-300 mg/mL, both Newtonian fluids, were tested using the microfluidic viscometer and found to generate data that favorably compared to that obtained using conventional rheometer. A Non-Newtonian fluid polyethylene oxide (PEO) fluid was also tested at a range of shear rates between 200-2000/s, and similarly found to compare favorably a conventional rheometer.
Two exemplary cartridge designs were constructed and tested, as described below. Ten to 30 microliters (ul) of sample fluid were used to generate and analyze the data represented herein. Variable pressures in a range of range of 2000-20,000 Pa were applied to each sample fluid as indicated. Tests were run on channels that very closely resemble Cartridge and Cartridge 2, however the dimensions were not precisely as described for each cartridge. All experiments were carried out at 25° C.
In one cartridge iteration (“Cartridge 1”, illustrated in
For the glycerol comparison using Cartridge 1 (
In another cartridge iteration (Cartridge 2; illustrated in
For the glycerol comparison using Cartridge 2, each experimental data point comprises an average of at least six runs and is compared against viscosity data collected from a commercially available rheometer instrument (DV2T by Ametek Brookfield). The PEO comparison data was collected at eight different shear rates and similarly compared against rheometer data. The rheometer data is limited because the instrument requires additional spindles to cover a wider shear rate range.
A comparison to conventional rheometry was also performed using a fluid comprising bovine serum albumin (BSA) using Cartridge 2. Each experimental data point comprises an average of at least six runs and is compared against viscosity data collected from a commercially available rheometer instrument (DV2T by Ametek Brookfield). The results are shown below and confirm that the microfluidic viscometer can be used for fluids comprising proteins.
A comparison to conventional rheometry was also performed using a fluid comprising monoclonal antibodies (mAb) using Cartridge 2. Each experimental data point comprises an average of at least six runs and is compared against viscosity data collected from a commercially available rheometer instrument (DV2T by Ametek Brookfield). The results are shown below and further confirm that the microfluidic viscometer can be used for fluids comprising proteins.
The present study demonstrated the ability of the microfluidic viscometers disclosed herein to measure the viscosity of Newtonian and Non-Newtonian fluids over a wide range of shear rates, and concentrations. Furthermore, the microfluidic viscometers disclosed herein are shown to minimize fluid sample volume down to 10 μL, allows for easy multiplexing capabilities, and generates highly accurate results.
Those skilled in the art can devise many modifications and other embodiments within the scope and spirit of the present disclosure. Indeed, variations in the materials, methods, drawings, experiments, examples, and embodiments described may be made by skilled artisans without changing the fundamental aspects of the present disclosure. Any of the disclosed embodiments can be used in combination with any other disclosed embodiment.
In some instances, some concepts have been described with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the aspects and embodiments herein.
This application claims the benefit of U.S. Ser. No. 62/755,320 filed on Nov. 2, 2018, which is incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2019/059504 | 11/1/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62755320 | Nov 2018 | US |
